To give you a simple answer, the CA does and usually will tell our FAs to provide water and snack service.

The problem is the CA doesn't have the final authority anymore to delay boarding or deplane the aircraft (unless it's an emergency obviously). So for example, it's leg 3 of 4 flying out of a G4 base in Florida. A situation arises where there is an inoperative APU (which is common here). Then another MX problem occurs and we have to wait for a mechanic. The CA suspects it's probably a good idea to deplane, but someone in Ops that's obsessed with OTP in SFB or Vegas pulls rank and says no. After some back and forth with the company, the mechanic arrives and confirms with the CA that the problem could take awhile to fix (which the CA has probably been trying to tell operations about, but of course they wont listen). At this point 2.5 hours have passed its 105 degrees in back when they finally decide to deplane and of course the pax are livid (and rightfully so). Before long the crew times out and after 5 hours of waiting the flight is cancelled.

The above scenario is fabricated, but guys flying the line can attest that it's pretty atypical of how these huge delays happen. One hand doesn't talk to the other, and the powers that be would rather show the pilots who is in charge instead of working with us.